This invention relates generally to wood replacement materials (i.e., materials suitable for use as a replacement for natural wood) and more particularly to composite wood replacement articles and extrusion processes for forming such articles.
Although wood is a naturally reproducible resource, the supply of good wood for construction and other purposes is diminishing because of a large worldwide demand for wood products. Accordingly, there is increasing interest in developing wood replacement products. Wood composites represent one such replacement product. Wood composites comprising a combination of recycled wood scraps (such as wood meal, wood chips, sawdust, newspapers and the like, which are by-products of industrial processes and other industries using natural wood products) and a thermoplastic material have been known for many years. Generally, these composites are formed so that they may be used in many of the same applications as natural wood products, while offering advantages such as high resistance to rot, insects, and moisture. These products can have the same workability as wood and are typically splinter-free.
It is common with wood composites to include various additives to protect against discoloration, mildew, ultraviolet light exposure, etc. However, such additives can be very expensive, particularly when the additives are incorporated throughout the entire wood composite component. To address the high cost of these additives, multi-layer or laminated wood composite products comprising a substrate layer and a thin cap layer disposed on at least one surface of the substrate layer have been proposed. The substrate layer comprises a polymer/fiber mixture that produces the primary advantages of wood composites, i.e., wood-like stiffness and strength and low contraction and expansion. The cap layer comprises a mixture of polymer and additives, such as pigments and stabilizers, for protecting the substrate layer. By limiting the additives to the thin cap layer, this approach reduces the amount and cost of the additives while still providing the desired protection. A drawback of these laminated wood composites, however, is that the distinct cap layer can be susceptible to delamination and/or a negative market perception.